Tires and other rubber based articles are vulcanized or cured through the application of heat to the article. For example, tire molds make use of an expandable bladder and steam to apply heat and pressure to an uncured tire to vulcanize the tire and add features to the tire such as various tread designs. The time, pressure, and temperature are carefully controlled in an effort to obtain the desired amount of curing, which can occur both during and after the molding process.
Control of the degree of curing is particularly challenging with a rubber article that has a non-uniform shape or composition. For example, large tires (e.g., truck, aircraft, farm, off-the road) frequently have multiple, large tread features of varying shape and the overall tire may have multiple layers of different rubber compositions. This variance in composition, structure, and geometry frequently complicates the tasks of determining the amount of time and temperature to achieve proper cure of the tire without unnecessarily over-curing certain parts of the tire or using more production time per tire than needed.
Improvements to the curing process have been achieved by adding heating elements (also referred to as “curing elements”) to the mold based on the cure limiting parts of the rubber article. “Cure limiting” refers to the parts of the rubber article that are difficult to cure or take the longest to cure due to the article's heat transfer characteristics, composition, and/or geometry. For example, based on an identification of the cure limiting parts of the rubber article, WO 2007/037778 describes the addition of heating elements to a mold to enhance the transfer of heat into these cure-limiting zones and provide a more optimum cure.
The addition of heating elements to a mold provides certain challenges. One such challenge is the optimal positioning of the heating element and, more particularly, the optimal configuration of multiple heating elements. More specifically, it is desirable to optimize the number and configuration of heating elements in a mold so as to maximize heat transfer efficiency and reduce the overall duration of the curing time. Reductions in curing time can lead to a higher production rate and/or less energy consumption. With an objective of reducing the overall tire molding time and improving the degree of vulcanization in cure limiting parts of the tire such as the tread, a method of optimizing the location of a heating element within the tread would be useful.
Optimization can prove particularly difficult when the article to be cured is non-uniform as previously described. For example, the non-uniformities found in some tread patterns, particularly with large tires, presents unique problems in determining the heat transfer behavior during the transient conditions of the tire curing process. While heat transfer models can be developed for solution by finite element analysis, the computation time required to provide solutions for a non-uniform rubber article may not be practical—particularly when a configuration of multiple heating elements is being optimized. Moreover, the heat transfer characteristics will likely change with differences in tread patterns such as e.g., the shape and thickness of lugs or blocks in the tread—requiring a different analysis in each case. Therefore, an expedient method of optimizing the location of one or more heating elements within a tire or other rubber-based article of manufacture would be particularly useful.